I'd go with the Edge 830. The X30 series is a huge step up from the 520 you have been using. 20hr battery life (more if you disable Bluetooth and put it in battery save mode) is so nice for bikepacking and the small battery inside recharges quickly. I've yet to lose a ride from the latest gen Edges.
Regarding navigating a course backwards, you can modify the course on a computer or phone app, or if you don't need turn by turn prompts, just set it to "always display" under course settings. Then it's just a line on your map you can follow. It won't tell you you're off course, but sometimes it's better that way.